Conventionally, as a pressure storage device or a pulse pressure damping device, an accumulator provided with a metal bellows is used. In this type of accumulator, for example as shown in Patent Citation 1, a cylindrical metal bellows is arranged in a pressure container in which a shell and a lid body are integrated by welding or the like. One end of the metal bellows is closed by a cap, and the pressure container is divided into a gas chamber and a liquid chamber by the metal bellows and the cap. In a housing, a substantially cup-shaped stay having a through hole formed in the center of its bottom part is arranged upside down. When the metal bellows is compressed by gas pressure in accordance with the reduction of the pressure in the liquid chamber, a lower end of the cap is supported by the stay. Thus, even when the pressure of the liquid chamber is lowered, the metal bellows is maintained to have desired length by the stay. A sealing rubber is attached to a lower part of the cap. The sealing rubber has an annular projecting part provided with an oblique side part on the inner diameter side, another oblique side part on the outer diameter side, and a flat part coupling both the oblique side parts.
When stored pressure is discharged from an oil port, the cap is moved toward the stay by the gas pressure, and the annular projecting part is abutted with the bottom part of the stay and crushed up so as to seal a part around the through hole. In detail, after the flat part serving as a sealing part of the annular projecting part is abutted with the bottom part of the stay, the annular projecting part is crushed up, and in addition to the flat part serving as the sealing part, the oblique side part on the inner diameter side serving as a buffering part is also brought into a state where the oblique side part is closely attached to the bottom part of the stay. This state is called as a zero-down state. Therefore, by the metal bellows and the stay, the liquid chamber is partitioned into a closed liquid chamber between the inner side of the metal bellows and the outer side of the stay and an open liquid chamber positioned on the inner side of the stay, the open liquid chamber communicating with the oil port.
In such a way, in the zero-down state where the cap is abutted with the bottom part of the stay, the closed liquid chamber is formed between a stay outer peripheral face and the metal bellows. Even when the gas pressure acts on the metal bellows from the outer side, liquid pressure acts from the inner side. Thus, without generating great pressure imbalance in the metal bellows, damage to the metal bellows can be suppressed. When the zero-down state shifts to a normal operation state, the liquid pressure held in the closed liquid chamber formed between the stay outer peripheral face and the metal bellows acts in the direction in which the cap is separated from the stay as so-called pressurization, so as to contribute to the separation of the cap from the stay.